Device Nags You to Sit Up Straight

LumoBack Sensor Vibrates Whenever You Slouch

"Sit up straight. Put your shoulders back. Don't slouch." Chances are good that you've heard nags like these from your mother more than a few times in your life.

This week, I tested a gadget that might give mothers a rest. It's a $150 sensor called LumoBack, from a company called Lumo BodyTech, that straps around your lower waist to track your posture and vibrates whenever you slouch. It also tracks steps while walking and...